1. Field of the Invention
The present invention relates in general to dump trailers having a containment tub that can be emptied from either of its sides rather than from its rear end and more specifically relates to a lift system for the tub that is designed to better distribute pressure being exerted on the tub ends during the dumping process.
2. Description of the Prior Art
Bidirectional side dump trailers that include a pivotally mounted containment tub to permit dumping of a load from either side of a trailer rather than the trailer rear end have been known in the prior art for many years and have achieved acceptance in the marketplace since the early 1990's. Such trailers are particularly useful in situations such as during road construction when it is often necessary to dump numerous large loads of rock or gravel along the sides of roadbeds or for conducting ground leveling activity.
A variety of different types of bidirectional side dump trailers are known in the art. An example of one of the earlier types of side dump trailers used commercially is disclosed in U.S. Pat. No. 5,480,214 issued to Rogers. To provide for pivotal movement of the containment tub for dumping purposes, the Rogers' patent discloses the employment of hydraulic powered cylinders at the front and rear of the tub that when engaged cause the tub to pivot to one side or the other to dump material contained therein.
Although the Rogers' type of lifting system for the trailer tub has proved useful, it suffers from a number of deficiencies. Firstly and most importantly, by having the powered cylinders located at opposite ends of the containment tub, the lifting force applied, is placed upon the ends of the tub body as it is pivoted to one side or another by the cylinders, rather than being distributed along the length of the body. Secondly, the application of pressure on the ends of the containment tub often results in tub corner cracking as a result of the localization of lifting pressure thereon. Thirdly, the Rogers' design does not allow for the use of containment tubs that are longer than the trailer frame and, in many instances, it is beneficial to be able to use longer tubs when the hauling of maximum loads is required.
As an alternative to the Rogers' trailer design, lift systems for the containment tub have been developed that are positioned directly beneath the tub intermediate its end to provide a centrally directly lifting force oh the tub. Two such lift systems are disclosed in U.S. Pat. Nos. 5,906,417 and 5,597,211 issued to Golden.
Each of the Golden embodiments involve a centrally disposed, powered, multi-stage cylinder arrangement that lies beneath the containment tub such that as it is actuated the tub is tilted to one side or the other depending upon the dumping action desired.
Although the embodiments disclosed by Golden seem to eliminate the deficiencies of having end located power cylinders, as pointed out in the '211 patent, in column 10 due to the use of a single connection point between the lift system and the container tub, the stress on the base wall of the containment tub is extreme and requires further structural strength for the tub. The present invention is adapted to provide a bidirectional side dump trailer that avoids the deficiencies of having end mounted power cylinders or that have only a single centrally located lift system.
In view of the foregoing structure, it is an object of the present invention to provide a bidirectional side dump trailer with a lifting mechanism that distributes the lift force over a greater area to allow the associated stresses applied on the container tub to be minimized. Such distribution of the lift force presents the option to use lighter weight material (such as aluminum) in the containment tub ultimately providing greater payloads. It is a further advantage of the present invention to provide a lifting mechanism that requires a relatively low volume of hydraulic fluid for controlling the lift system. It is an additional object of the invention to provide a mechanism that not only allows for the possibility of a greater dump angle for the container tub, but also serves to locate the hydraulic cylinders of the lift mechanism in a location where they are protected beneath the containment tub.